Redundant switched full-duplex Ethernet type communication network

ABSTRACT

A redundant switched full-duplex Ethernet type communication network including at least two independent elementary networks, each elementary network including at least one source subscriber equipment and at least one destination subscriber equipment, connected to each other through at least one physical link through at least one switch, each equipment being connected to each of these elementary networks. A control performs a frame by frame redundancy on each elementary network.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent document is a divisional of U.S. application Ser. No.10/287,959 filed on Nov. 4, 2002, and claims priority on French patentapplication FR 01 14264 filed on Nov. 5, 2001, the entire contents ofeach of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a redundant switched full-duplex Ethernet typecommunication network, particularly in avionics.

2. Description of the Related Art

The Ethernet network, which is the reference in the world ofcommunication networks, can be used to send data in digital form bypackets or “frames”, where a frame is defined as being a set of datasent in a single step on the network.

In an Ethernet network, the data in each frame are not interpreted. Thenetwork carries the data without understanding their meaning. A frame iscomposed of two types of data, network data that are used to route theframe to its correct destination, and useful data which comprise the“useful load” in the frame.

An Ethernet network is composed of different equipment that issubscribed to the network, and connected to each other through acommunication means formed of active equipment called switches, whichperform three functions:

-   -   connect network subscribers in point to point mode through        physical links, which are physical supports for messages to be        exchanged, for example twisted pair cables,    -   route (switch) frames sent by source equipment to one or more        destination equipment,    -   check the integrity and the format of the Ethernet frame.

FIG. 1 illustrates an Ethernet network composed of two switches 11interconnected to each other and each connected to three items ofsubscriber equipment 12 in point to point mode.

Operation of such a network is simple. Each network subscriber can sendframes in digital form at any time towards one or several othersubscribers. When a switch receives the frames, the “networkinformation” data are analyzed to determine the destination equipment.The frames are then switched towards this equipment.

In the “switched full-duplex Ethernet type network” expression:

-   -   the “full-duplex” term means that the subscriber can send and        receive frames at the same time on the same link,    -   the “switched” term means that the frames are switched in        switches on appropriate outputs.

For example, this network may be a 100 Mbits/s switched full duplex typenetwork on twisted pair; the term “twisted pair” means that connectionsbetween the equipment and the switches are composed of two pairs ofcables, each pair being twisted; the term 100 Mbits/s simply means thetransmission or reception speed of frames on the network.

The Ethernet technology imposes:

-   -   a minimum size and a maximum size on the frames,    -   an identification of the source and/or the destination(s) in        each frame,    -   a CRC (“Cyclic Redundancy Check”) that checks the integrity of        the transported data.

At the present time, in the civil aeronautics field, data exchangesbetween the various onboard computers are based on the use of the ARINC429 aeronautical standard.

However, the switched full-duplex Ethernet network is frequently used inindustry. The emergence of new communication technologies shows thatthis type of network is an open and standard solution (IEEE standard802.3) with a considerable potential for development as a local network.But this type of solution does not provide any means of guaranteeingsegregation and transfer performances (in terms of throughput, latency,etc.) necessary for avionics applications.

The purpose of this invention is to improve the availability of such anetwork, by providing means of protecting against the loss of a link ora switch, to enable its use in avionics.

In general, in a distributed control system, the communication system ismade redundant so that each node in a set of nodes (equipment) can becontrolled from one of these nodes, and so that these nodes can beconnected so as to increase the load factor on the system and thereforeits efficiency.

A European patent application EP-0 854 610 describes an Ethernetcommunication redundancy process between a set of nodes forming such adistributed control system. These nodes are connected to each other induplex through communication lines in a first and a second Ethernetnetwork, that are independent from each other. At the transmission end,a first node transmits identical data on communication lines in thefirst and the second networks, a data identifier being added to thetransmitted data. A second node at the reception end determines which ofthe identical data received from the first node through communicationlines in the first and the second networks arrived first and uses it asthe reception data. The second data are then rejected if they areidentical to the first data.

Unlike the process described in this patent application which isapplicable to data, the purpose of the invention is to make a processenabling frame by frame redundancy.

SUMMARY OF THE INVENTION

The invention relates to a redundant switched full-duplex Ethernet typecommunication network including at least two independent elementarynetworks, each including at least one source subscriber equipment and atleast one destination subscriber equipment, connected to each otherthrough at least one physical link and through at least one switch, eachequipment being connected to each elementary network. A control performsa frame by frame redundancy on each elementary network.

In the network, the control in transmission:

-   -   adds a numbering field in each transmitted frame, to insert a        frame number, and    -   sends this frame on each of the elementary networks.

In reception the control:

-   -   stores the received frame number,    -   accepts this frame only if its number has not already been        received.

Advantageously, the accepting of a frame takes place during a given timewindow.

In one advantageously embodiment, the virtual link concept is used,which is a conceptual view of a link from one source equipment to atleast one destination equipment. A virtual link number is accepted inthe numbering field of each transmitted frame. A virtual link ischaracterized by:

-   -   a transfer direction, the virtual link being single directional,    -   a source equipment,    -   one or several items of destination equipment,    -   a fixed passband,    -   a maximum guaranteed time for transfer of packets from a source        equipment to a destination equipment,    -   a path fixed on the network,    -   a unique identifier.

Advantageously, the invention can be used for implementing a redundantswitched full-duplex Ethernet type communication network in avionics.

This type of network redundancy, which may for example include doublingup the network, with each subscriber being connected to each of the twonetworks, one of the two packets being selected on reception, canincrease the network availability; the network will continue to operateif it has one or several defective switches or links.

The invention can achieve redundancies of order 2 or more, independentlyof the communication stack and applications.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates an Ethernet network according to known art,

FIG. 2 illustrates the concept of a virtual link in an Ethernet networkaccording to known art,

FIG. 3 illustrates an Ethernet network according to known art in whichseveral virtual links are shown,

FIG. 4 illustrates services used in the process according to theinvention,

FIG. 5 illustrates an example of second order redundancy in subscribedequipment according to the invention,

FIGS. 6A and 6B illustrate operation of the process according to theinvention in transmission mode and in reception mode respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention relates to an implementation of a redundant switchedfull-duplex Ethernet type communication network comprising at least 2elementary networks each of which comprises at least one sourcesubscriber equipment and at least one destination subscriber equipmentconnected to each other through at least one physical link. In thereminder of the description, we will consider two elementary networksRE1 and RE2 as a non-limitative example. A frame by frame redundancy isperformed on each of the elementary networks.

In transmission, the network:

-   -   adds a numbering field in each transmitted frame, to insert a        frame number so that each frame can be identified in time,    -   sends this frame on each of the elementary networks.

In reception, the network:

-   -   stores the received frame number,    -   accepts this frame only if its number has not already been        received.

Advantageously, the frame acceptance only takes place during a giventime window, so that only a limited memory size can be used, each framenumber reappearing after a determined time.

Therefore, the invention only sends the first frame received from anelementary network, to the application considered, the othercorresponding frames from other elementary networks being rejected.

FIG. 5 illustrates an example of a second order redundancy used in asubscriber equipment.

In one advantageous embodiment, the invention uses the virtual linkconcept to limit the end to end transfer time, in other words sourceequipment towards one or several destination equipment.

This virtual link (VL) concept provides means of isolating datatransfers between a source equipment 13 and destination equipment 14. Avirtual link VL is seen as a “pipe” on the network, as illustrated inFIG. 2.

A virtual link VL is characterized by:

-   -   a transfer direction, the virtual link being single directional,    -   a single source equipment 13,    -   one or several destination equipment 14,    -   a fixed passband (maximum number of packets and their size per        second),    -   a maximum guaranteed time for transfer of packets from a source        equipment 13 to a destination equipment 14, regardless of the        behavior of the rest of the network, each virtual link having        its own transfer time,    -   a path fixed on the network,    -   a unique identifier.

A network subscriber may comprise several virtual links VL1, VL2, VL3,as shown in FIG. 3. We have:

-   -   a virtual link VL1 from equipment 21 to equipment 23, 24 and 25,    -   a virtual link VL2 from equipment 21 to equipment 22 and 23,    -   a virtual link VL3 from equipment 23 to equipment 22.

When equipment 21 wants to send a packet to equipment 23, 24 and 25, itsends a packet on the virtual link VL1. When it wants to send a packetto equipment 22 and 23, it sends a packet on the virtual link VL2.

The difference between virtual links VL1 and VL2 is identified by thedestination identifier in the packet. On the network, the virtual linkto which a packet belongs is determined by the identifier of the virtuallink in the packet.

A switch uses a static configuration table to determine the virtuallinks that it is required to switch, and the allowable number of packetsfor a virtual link.

The virtual link concept is a means of fixing communications betweenequipment by configuring routes and passbands allocated to the virtuallinks. Thus, the flow formed by a virtual link is sure to be notdisturbed by other flows sharing the same physical links all along itsroute in the network.

Furthermore, the virtual link concept enables central flow management,to make sure that the sum of the passbands allocated to virtual links onthe same physical link does not exceed the capacities of the technologyof this physical link. In the above example, the sum of the passbands ofvirtual links VL1 and VL2 must be less than the transmission capacity ofthe physical link from equipment 21.

Therefore, a virtual link is a conceptual representation of a link froma transmitter equipment to one or several items of receiver equipmentthat have the following characteristics:

-   -   fixed and predetermined route on the network,    -   fixed and guaranteed passband,    -   maximum guaranteed end to end latency    -   explicit identification in a multidestination or “multicast”        type Ethernet frame (multidestination MAC address) and this        identification is kept when passing through one or more        switches.

As illustrated in FIG. 4, the invention is then characterized by theimplementation of several services in each subscriber equipment 50:

-   -   a transmission service, the role of which is to enable an        application 52 to access virtual links in transmission (virtual        links VL1 and VL2). This service multiplexes virtual links        towards a physical link through an Ethernet interface, and for        each virtual link sends packets as a function of the passband        allocated to the virtual link.    -   A reception service 55 that decodes frames (virtual links VL21        and VL22), checks their format and makes useful data available        to applications.

In these transmission and reception services, the application may treata virtual link like a queue.

Other protection services help to guard against some network failures.

A service for protection of a passband in the switch, which for eachincoming virtual link is capable of checking the time characteristics ofpackets (spacing between packets, the consumed passband). If theallowable characteristics are exceeded, the packets are simply destroyedto prevent a failure in a transmitter or a virtual link from adverselyaffecting traffic in other virtual links starting from this switch.

A subscriber network redundancy service 60 that sends and receives eachframe on the two elementary networks RE1 and RE2, in order to implementnetwork redundancy. This network duplication in two elementary networksRE1 and RE2, that is transparent for applications, provides a means ofguarding against a failure in a switch or an interface (it does notreplace system level redundancy). This network redundancy service 60 isconnected to at least one first Ethernet interface 61 with theelementary network RE1, and a second Ethernet interface 62 with theelementary network RE2.

As shown in FIG. 5, the equipment in the invention to obtain redundancyof virtual links on the physical layer comprises at least two physicalinterfaces, so that they can be connected to at least two independentelementary networks RE1 and RE2. Their communication stacks includeredundancy mechanisms that enable:

-   -   sending an identical frame on the elementary networks RE1 and        RE2,    -   selecting the first valid received frame.

Therefore, in this embodiment, the invention used in the subscriberequipment and applied by a virtual link onto the network are such that:

-   -   in transmission, for each frame received from the communication        stack:    -   a numbering field is added so that a counter numbers the frame        corresponding to each virtual link,    -   this frame is sent onto the elementary networks RE1 and RE2.    -   in reception, for each frame assigned to a virtual link:    -   the frame number is stored,    -   this frame is accepted if this number has not already been        received, and if it is received it is destroyed.

FIG. 6A illustrates this embodiment of the invention in transmission,and 6B illustrates it in reception.

FIG. 6A illustrates the following in sequence:

-   -   addition of a numbering field on the IP/UDP/data assembly,    -   numbering of the frame for each virtual link,    -   send the frame to each Ethernet controller that formats it as an        IEEE 802.3 frame.

Numbering is done by virtual link, and the same number can be used fortwo different virtual links.

FIG. 6B shows the following in sequence:

-   -   for each virtual link, verification of the number in the        numbering field,    -   the frame is eliminated if the number has already been received,    -   otherwise the frame is sent to the higher layer.

The counter field can be small, and when the counter reaches its maximumvalue, frame numbering restarts from zero.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

1. A redundant switched full-duplex Ethernet communication networkcomprising: at least two independent elementary networks, eachelementary network comprising at least one source subscriber equipmentand at least one destination subscriber equipment; at least one switchconfigured to connect the at least two independent elementary networksto each other through at least one physical link, each equipment beingconnected to each of said two independent elementary networks a controlconfigured to perform a frame by frame redundancy on each elementarynetwork; and a virtual link mechanism configured to limit a transfertime from said at least one source subscriber equipment to said at leastone destination subscriber equipment, wherein said at least one switchis configured to rely on a configuration table to identify a virtuallink to be switched and to further identify a number of packets for saidvirtual link.
 2. A network process according to claim 1, wherein thereare two independent elementary networks.
 3. A network according to claim1, wherein the control performs the frame by frame redundancy by beingfurther configured to, in transmission: add a numbering field in eachtransmitted frame, to insert a frame number; and send the frame with theinserted frame member on each of the elementary networks.
 4. A networkprocess according to claim 3, wherein the control performs the frame byframe redundancy by being further configured to, in reception: store thereceived frame number; and accept the frame only if its frame number hasnot already been received.
 5. A network according to claim 4, in whichthe control is further configured to accept a frame only if it takesplace within a given time window.
 6. A network according to claim 4,wherein said virtual link concept is a conceptual view of a link fromsaid at least one source subscriber equipment to said at least onedestination subscriber equipment.
 7. A network according to claim 6,wherein a virtual link number is accepted in a numbering field.
 8. Anetwork according to claim 6, in which said virtual link comprises: atransfer direction, the virtual link being single directional; a sourceequipment; one or plural items of destination equipment; a fixedpassband; a maximum guaranteed time for transfer of packets from asource equipment to a destination equipment; a fixed path on thenetwork; and a unique identifier.
 9. A network according to claim 1 thatis used for implementation of a redundant switched full-duplex Ethernettype communication network in avionics.
 10. A redundant switchedfull-duplex Ethernet communication network comprising: at least twoindependent elementary networks, each elementary network comprising atleast one source subscriber equipment and at least one destinationsubscriber equipment; at least one switch configured to connect the atleast two independent elementary networks to each other through the atleast one physical link through at least one switch, each equipmentbeing connected to each of said two independent elementary networks;means for performing a frame by frame redundancy on each elementarynetwork, and a virtual link mechanism configured to limit a transfertime from said at least one source subscriber equipment to said at leastone destination subscriber equipment, wherein said at least one switchis configured to rely on a configuration table to identify a virtuallink to be switched and to further identify a number of packets for saidvirtual link.
 11. A network process according to claim 10, wherein thereare two elementary networks.
 12. A network according to claim 10,wherein the means for performing performs the frame by frame redundancyby being further configured to, in transmission: add a numbering fieldin each transmitted frame, to insert a frame number; and send the framewith the inserted frame member on each of the elementary networks.
 13. Anetwork process according to claim 12, wherein the means for performingperforms the frame by frame redundancy by being further configured to,in reception: store the received frame number; and accept the frame onlyif its frame number has not already been received.
 14. A networkaccording to claim 13, in which the means for performing further acceptsa frame only if it takes place within a given time window.
 15. A networkaccording to claim 13, wherein said virtual link is a conceptual view ofa link from said at least one source subscriber equipment to said atleast one destination subscriber equipment.
 16. A network according toclaim 15, wherein a virtual link number is accepted in a numberingfield.
 17. A network according to claim 15, in which said virtual linkcomprises: a transfer direction, the virtual link being singledirectional; a source equipment; one or plural items of destinationequipment; a fixed passband; a maximum guaranteed time for transfer ofpackets from a source equipment to a destination equipment; a fixed pathon the network; and a unique identifier.
 18. A network according toclaim 10 that is used for implementation of a redundant switchedfull-duplex Ethernet type communication network in avionics.